The World Health Organization recommends consumption of at least 20 liters of fresh water per day for individual survival. When considering infrastructure and communal needs, such as those of schools and hospitals, the necessary fresh water consumption level for individual survival is approximately 50 liters per person per day. While the consumption rate per individual for a number of African countries is at the WHO consumption recommendation level of 20 liters, in other western countries, the fresh water consumption level reaches only 150 liters per day. In the United States, people consume on average up to 400 liters of freshwater per day. As such, with the rising population, industrialization of developing nations, and overall increase in quality of life throughout most parts of the world, fresh water consumption levels continue to rise. In fact, it is estimated that by the year 2040, demand for fresh water will surpass the available supply.
Compounding this problem is the growing contamination of fresh water sources, which only comprise about 2.5 percent of the total water on earth. Of that 2.5 percent, only 0.5 percent of the total fresh water available is found in easily accessible sources such as lakes, rivers and aquifers. The remainder of the total fresh water sources is in frozen form in glaciers.
Moreover, populated areas struck by natural disasters are faced with a great need to quickly supply potable water to the victims for drinking, cooking, and sanitation purposes. In industrialized nations, the fresh water infrastructure normally relied on is often damaged or contaminated to the point that it cannot be used in the immediate recovery period after the devastation of such an event. In contrast, a fresh water infrastructure might not even exist in developing nations, making the acquisition and distribution of potable water all the more difficult. Thus, while the scarcity of potable water is a growing problem worldwide, it is particularly concerning in arid regions and among developing countries.
According to the United Nations Atlas of the Oceans, more than 44 percent of the world's inhabitants live within 150 kilometers of the coast. This 44 percent accounts for more people than there were in the entire world just 60 years ago. In the United States, 53 percent of the population lives near the coast. In another 30 years, it is estimated that over 70 percent of the population will be coastal. The crowding of the population in any particular area necessarily leads to overexploitation of regional resources, which, in this context, includes fresh water. Given the number of people within proximity of the coast and the sea, it would be beneficial to turn to the sea for fresh water.
However, in contrast to the 1,500 parts per million (ppm) in total dissolved solids (TDS) contained by fresh water, sea water ranges from 10,000-45,000 ppm in TDS, with 35,000 TDS being the standard reference [Cipollina et al., 2009]. The United States Environmental Protection Agency recommends an upper limit of 500 ppm for drinking water.
With such a large amount of non-potable water available (sea water comprises about 97.5 percent of the total water on earth), increased effort has been made in recent years to scale up desalination. However, while methods exist to desalinate water, the current processes require a significant amount of energy. FIG. 1 explores the various types of renewable energy (RE) technologies and the relationship to particular desalination processes. While some RE technologies are in commercial operation today (e.g., solar energy and wind energy are proven sources of RE that can provide electricity to any electrically driven desalination system), others have yet to be demonstrated and those that are in commercial operation are still in need of refinement. For example, tidal and wave energy have very recently begun to show much promise, but are still in early phases of commercialization.
Based on the potential future lack of potable water in overpopulated areas, contaminated water in times of disaster, and locations with no fresh water infrastructure, there is a need in the art for large scale potable water production that minimizes energy consumption. In addition, with the lack of available fresh water sources from which to retrieve potable water, the extremely high coastal populations, and rising energy prices, pairing potable water production from the sea with renewable energy is also needed.